Setting a SCSI ID using jumpers (1 = shorted, 0 = open): On a three-bit jumper block, which bit pattern selects logical ID 3?

Introduction / Context:
Legacy SCSI devices use hardware jumpers or DIP switches to set the device ID. Understanding binary weighting of the ID bits is essential when configuring multiple devices on the same bus to avoid conflicts and ensure proper enumeration by the host adapter.

Given Data / Assumptions:

• Three ID bits are available, representing values 1, 2, and 4 (least to most significant).
• Convention: 1 = jumper shorted (logic high), 0 = open (logic low).
• Target ID is decimal 3.

Concept / Approach:
Binary representation maps decimal numbers to powers of two. Decimal 3 equals 2 + 1, which corresponds to setting the least significant two bits to 1 and the most significant to 0 when using a 3-bit field: 011 in binary (MSB to LSB). This pattern will program the device to ID 3 on the SCSI bus.

Step-by-Step Solution:

Verification / Alternative check:
Cross-check with the drive’s label or manual showing ID tables; 011 is universally shown for ID 3 on 3-bit SCSI ID blocks.

Why Other Options Are Wrong:

• 100: Selects ID 4 (only MSB set).
• 010: Selects ID 2 (only the middle bit set).
• 101: Selects ID 5 (4 + 1).
• None of the above: Incorrect since 011 is valid for ID 3.

Common Pitfalls:
Reading bit order right-to-left incorrectly, mixing up the position of MSB/LSB on the header, and forgetting to remove termination on middle-of-bus devices.

Final Answer:
011